There are many different ways to classify pain. Generally it is classified according to its location, duration, frequency, underlying cause and intensity. Here you can find further information on some of the classifications.
Classification of pain is thus complicated and can be a source of confusion for many clinicians. As a result, many practitioners now frequently use several different classification systems. Clear distinctions between these systems are not always possible: the more simplistic the classification of pain, the greater the number of omissions and overlaps that can occur.1
1 Pasero C, Paice JA, McCaffery M. Basic mechanisms underlying the causes and effects of pain. In: McCaffery M, Pasero CL, editors. Pain: clinical manual. 2nd ed. St. Louis: Mosby; 1999:15-34.